In the paper-making industry, a variety of additives are incorporated to achieve one property or another. Generally, however, the paper products are all characterized by a common ingredient and property -- cellulosic fibers which are held together by hydrogn bonding. Because of this, binders are not incorporated as such.
The main disadvantage of cellulosic fibers is their combustibility and specifically the smoke generated therefrom. Stringent fire codes prohibit in certain instances the use of such paper even as cover sheets for gypsum wallboard, which is otherwise noncombustible, because of the combustibility of the cellulosic fibers. Fireproofing agents are undesirable additives due to their expense and inability to eliminate the smoke hazard from wallboard.
A recent paper product disclosed in U.S. Pat. No. 3,562,097 incorporates mineral fibers in a paper designed especially for the paper cover sheets of gypsum wallboard. However, the usual cellulosic fibers are also included, although in lesser amounts, so that no binder is necessary or even disclosed. The resultant product, although superior in having increased porosity, still has cellulosic fibers that tend to render the product more combustible than would be the case without the cellulosic fibers. Yet, attempts to eliminate the cellulosic fibers from the paper disclosed in the aforesaid patent have resulted in a "sheet" which does not hold together. This is not surprising, as mineral or inorganic fibers lack the capability of being hydrated or bonded together by hydrogen bonding.
A highly refined gel has been used in board products in the past, some of which have incorporated mineral fibers, among other ingredients. Examples of these are disclosed in U.S. Pat. Nos. 2,773,763 and 3,494,824. However, in each case the product has been an insulation or acoustical board having thicknesses on the order of 5/8 of an inch. Obviously, such boards are not suitable as paper or paper sheets, and cannot be used as such.